| Summary: | Phenological responses are among the most well-demonstrated plant responses to global change. Advancing springs have been demonstrated across temperate regions as springs warm and winters shorten. These responses result in a cascade of ecosystem consequences, yet whether they increase plant performance is unclear. Though earlier leaf development in spring may increase total productivity across the growing season, this assumes that leaf senescence in the fall will similarly take advantage of warmer falls. However, little attention has been paid to later phenophases, and some evidence points toward advancing, rather than delayed leaf senescence in the fall. This seems especially true at high latitudes, where Arctic species respond strongly in spring but may shift their entire growing season earlier. In contrast, invasive species or encroaching shrubs appear more able to capitalize on a longer potential growing season. In this thesis, I examine plant phenological responses to variation in their environment, with a particular focus on leaf senescence. In Chapter 1, I examine how variation between three years of phenological data reveals weakened end-of-season phenological responses relative to start-of-season leaf-out. In Chapter 2, I expand on these results by integrating data on light competition and linkages between reproductive and vegetative phenology. Finally, in Chapter 3 I perform a controlled experiment in growth chambers to examine if leaf senescence responds not only to climate but also to photoperiod, to uncover whether the apparent lack of end-of-season response in Chapter 1 could be related to daylength, a variable that is difficult to test in the field. Overall, this thesis demonstrates that leaf senescence is more conserved, and perhaps more multivariate than leaf-out in spring. Additionally, phenophase transitions appear to be somewhat linked, with spring leafing-out and flowering phenology both influencing the timing of leaf senescence. While the field data I analyzed were unable to detect large ...
|
|---|